Power transmission system including pressure fluid follow-up servomotor



May 1948' M. K. ENGDLDBY ET AL POWER TRANSMISSION SYSTEM INCLUDING PRESSURE FLUID FOLLOW-UP SERVOMOTOR 4 Sheets-Sheet 1 Filed March 19, 1942 mfma 5! Jam Hi Porn:

- ay 4, 1943- M. K. INGOLDBY Er AL 2,440,687

-UP SERVO-MOTOR POWER TRANSMISSION SYSTEM INCLUDING PRESSURE FLUID FOLLOW Filed March 19, 1942 4 Sheets-Sheet 2 MQ w awm

7uven irors JZMMMM May 4, 194 M. K. INGOLDBY ET AL POWER TRANSMISSION SYSTEM INCLUDING PRESSURE FLUID FOLLOW-UP SERVO-MOTOR Filed March 19, 1942 4 Sheets-Sheet 3 7 iljd fla May 4, K. INGQLDBY r AL POWER TRANSMISSION SYSTEM INCLUDING PRESSURE FLUID FOLLOW-UP SERVO-MOTOR Filed March 19, 1942 4 Sheets-Sheet 4 Q} nveniors 1% ?MM a, JQ M receiver is of course reduced with Patented May 4, 1948 POWER TRANSMIS SION SYSTEM IN OLUDING FOLLOW-UP SERVO- PRESSURE FLUID MOTOR Maurice Kerr lngoldby, deceased, late of Tynemouth, England, by Thomas Frederick Clarke,

Swanley, and Percy William Cole,

land, executors,

Parley, Engand Johann Hermann Abbink- Spaink, Jesmond, Newcastle-on-Tyne 2, England, assignora to Vickers-Armstronzs Limited,

London, England,

a British company Application March 19, 1942, seriaigllo. 435,356

In Great Britain J line 9,

Claims, i

This invention relates to power transmission s stems of the repeater type for use in connection with the fire control of guns or for the control of the setting of other apparatus adapted to have imparted thereto changes in angle or direction, e. g. changes in the angle of elevation of a gun Up to the present many power transmission systems have been employed some of which use the well known Selsyn transmitter and receiving units. Customarily, the transmitter unit is operated from a director or other primary control device and the receiver is connected directly to the load which has to be operated according to the movements of the director. The load which is normally massive, cannot, of course, be up erated from the Selsyn receiver and for purposes of the power operation, a power drive of some suitable type is provided. Ihe power drive is arranged to be under the control of the Selsyn transmitter and receiver units, in the sense that when these units are not in alignment the power drive is brought into operation and continues to operate until alignment is achieved. With a system such as outlined, when the load approaches its alignment position, the relative displacement between the Selsyn transmitter and the Selsyn consequent reduction in the torque of the power drive. Hence, the synchronizing or ire-setting force tends to be reduced to zero as the load approaches the desired coincident position, with the result that the accuracy of the repeater as a whole may be very low. Moreover, the load may well move, by virtue of its massive nature, to a position where it has passed its position of coincidence correspondingto the director position. In such case the Selsyn transmitter and receiver units may cause a reversal of the power drive to the massive load in an attempt to recentre the latter and, as a result, the load may then be moved past the desired recenti'e position once more. Such a 1;! oscillation of the massive load can defeat whole object of the transmission system.

From the above it will be realised that if the power drive is not itself dead-beat in action, that is to say, if it permits the massive load to have a certain amount of lost motion, the transmission system including such power drive becomes valueless, The present invention provides a solution to the problem indicated above by the provision of an electric transmission system employing Selsyn units with a swashplate hydraulic power amplifier as the power drive for the masm: "or

sive load. The characteristics at a swashplate hydraulic power amplifier render the latter particularly suitable for a, combination in the manner indicated above, since such an amplifier is dead-beat in operation in the sense indicated above, and, moreover, the displacement of the control means or the amplifier produces at the output thereof a speed oi operation which is proportional to such displacement.

Referring to the drawings:

Figure l is a general arrangement diagrammatically illustrating a transmission system in accordanc with the invention;

Figure 2 illustrates a modified method of corresting for lag between the output or load drivingr shaft of the apparatus and the movement initiating means;

Figure 3 is a wiring diagram oi the system; and

Figure i: a sectional elevation through the hydraulic power amplifier.

In dcscrihhsg the constructional forms of transmission system. illustrated icy the accompanying drawings, it will he assumed that the apparatus is applied to the adjustment of a gun mounting. There is a director or any equivalent driving member operating a shaft i driving a shaft 2' carrying the rotor of one of a pair of Selsyn units 2 and 2 of standard design, and comprising the transmission end of the apparatus. The rotors or the 'Selsyn units i and. it are connected together by sear wheels 3 and 3 so that the movement of one produces a simultaneous movement of the other with a predetermined velocity ratio therehetween. For the sake of eX- ample, it will be supposed that for one revolution of the unit the unit 2 by virtue of the geared connection makes it revolutions, Then the unit 1 will be hereinafter referred to as the coarse unit whilst the unit 2, which has to make it revolutions for one revolution of the coarse unit, will he referred to hereinafter as the line unit. At the receiving end of the apparatus there are two further Selsyn units 5 and '3 which are precisely similar to the Selsyn units l and 2 employed at the transmitting end.

All the Selsyn units are supplied with phase alternating stator current from a suitable source of supply whilst all the rotors thereof are connected by way of slip-rings 3a with a thermionic amplifier l by cables 8, the cables supplying current to the amplifier being indicated by the reference numeral 9. The Selsyn units 5 and 5 of the receiving end are geared together by gear wheels ill and H with the same ratio as at the transmitting end, i. e. the 72:1

threeratio previously referred to. The fine unit 6 of the receiving end is mechanically coupled with the rotor of a, D. C. motor I2, the armature current of which is supplied by outputcables I3 leading from the amplifier I. The motor I2 is arranged to drive the gun mounting through the medium of an hydraulic power amplifier unit It of the swashplate type.

A suitable construction of power amplifier is shown in Figure 4 and is similar to that described in co-pending application Serial No. 435,348, now

Patent No. 2,428,025, and in which, when the input shaft I04 is turned initially, the centre member I02 of the differential gear will therefore be displaced and will cause a corresponding longitudinal displacement of the valve IN, to permit of the inflow of the operating fluid from a suitable source of supply, e. g. a hydraulic pump I26 (see Figure 1) which displacement will continue until the high torque output shaft III gains the speed of the input shaft I06, when the valve will remain in that position. The input shaft is mechanically connected with the output shaft by a shaft H2 forming a continuation of the output shaft, teeth II8 on the shaft II2 meshing with a pinion or pinions IIIi' rotatably mounted upon the side plate I I9. The differential gear also includes the usual planet pinions lit, the pinions I I4 and I It meshing with each other, 4 intum meshing with the gear wheel I03 carried by the input shaft I06, the pinions lid and 4' being rotatably mounted upon shafts connecting the members I02 and IIS together.

The input shaft I04 is driven by the electric motor I2 of Figure 1, whilst the output shaft I I I is driven by fluid pressure controlled by means of the valve IOI, the fluid entering the unit through the inlet connection M6 and after passing the valve, entering the cylinders I ll, the pressure of the fluid on the pistons in the cylinders imparting a rotational movement to the output shaft through the medium of the angle box, in-' dicated generally by the reference numeral M0, the output shaft being thus caused to rotate at high speed. The exhaust fluid returns to the source I26 by put shaft I to be turned clockwise, the gear member I03 attached thereto will rotate the pinion I It which in turn will, via the pinion M l, cause the crown wheel or centre member I02 to rotate in, say, a clockwise direction, pinion I0? thereby causing the hydraulic control valve Ifil to be given a combined sliding and rotary movement, admitting fluid to the cylinders Iii causing the angle box II8 to rotate the main output shaft III.

As in co-pending applications Serial Nos. 435,348 and 435,349, now Patents Nos. 2,428,025 and 2,412,366, the hydraulic power amplifier I0 is provided with a correction unit indicated generally by the reference numeral 2i (see Figure 1) this correction unit being a smaller edition of the hydraulic power amplifier I4 and having as its input shaft the shaft I 8 operating the valve IOI. Original Figure 4 of application Serial No. 435,348, and the single original figure of application Serial No. 435,349, both show a connection between the valve shaft of the hydraulic power amplifier and the correction unit which is the equivalent of that disclosed herein. In the present embodiment, the appropriate part of the shaft I I08 is divided to afiord a slidable connection I08a whereby the end of the shaft I08 operating the valve IOI can have translative movements imparted to it for actuating the valve WlthQllt I115 the conduit I It. Assuming the inplacing axially the end of the shaft I08 actin as the input shaft for the correction unit 2 I The translatlve movement of the valve operating end of the shaft I08 is obtained by reason of a worm I20 operating within a nut I2I fixed within the housing of the power amplifier It, the axial dimension of the pinion I01 being sumcient to cover this displacement of the shaft I08 to which it is splined without the pinion I01 disengaging from the gear member I02. The axial displacement of the appropriate end of the shaft I08 can be indicated by a pointer I22 operated from an abutment I23 on the shaft, the free end ofthis supply being regulated by a valve which op-,

erates within the housing of the unit 2I in a manner identical with the valve IOI of the power amplifier It, i. e. through a, differential gear forming a couple between the input shaft I08 and an output shaft 521, this output shaft being driven in the same manner as the output shaft III and carrying a pinion IZ'I' meshing with gear teeth I28 on the periphery of the casing 6a of the repeater unit 5.

When the input shaft I06 of the power amplifier I6 is initially rotated by motor I2, the centre member I02 of the differential gear not only shifts the valve IOI from its neutral position so as to start the hydraulic motor drive of output shaft ill, but also rotates the input shaft I08 of correction unit M, which in turn causes the output shaft I21 of said unit to be hydraulically driven and through the pinion I27 to rotate the stator do of the Selsyn receiver unit insuch a manner as to advance the rotor 6, motor I2 and shaft I00 with respect to the initiating shaft I of the transmitter and of the system in the same proportion that the output shaft III lags behind the input shaft I06.

The valve llil of the hydraulic amplifier It is, by the foregolngarrangement, adapted to be reset towards its zero position with the aid of the differential gear embodying the members I02, I03, IIB, lid and llil'. It will be apparent that contemporaneously with this adjustment of re-setting of the valve IOI the input shaft of the correction unit 2I will be rotated with consequent displacement of the valve appropriate to the unit 2i and actuation of the hydraulic motor of such unit, this resulting in the output shaft I27 having imparted thereto a movement proportional to lag between the input shaft Hill and output shaft III of the power amplifier It, the desired correction being derived from the fact that the motor I2 has its armature supplied with current in the one direction or the other corresponding to the direction of phase displacement arising out of the aforesaid adjustment of the casing to of the Selsyn unit a It will be noted that the main output shaft I I I is in driving connection with the toothed shaft IIZ which causes the planet pinion or pinions associated therewith to rotate, which in turn causes the crown wheel I02 to rotate in an anticlockwise direction, thereby restoring the sliding valve 1i0I to its original position and bringkeep the shaft IH rotating, it is necessary to continue to rotate the input shaft "M.

It will further be appreciated that the relative angular displacement between the shaft HM and shaft Ill by the diilerential gear determines the amount of valve opening of the sliding valve NIH, and therefore that for a given output torque, any increase in the speed of shaft ill is due to an increase in the lag or angular displacement between shafts I04 and iii.

The lag between the shafts represents a, measure of the rate oi angular displacement of the output shaft i it when the latter and the input shait are operating in synchronism- A change in velocity of input will momentarily increase such lag andresult in alteration or the velocity of the output. Known swash plate engines of the kind here concerned are in themselves practically dead-beat in action in the sense that a displacement of the control valve till produces a proportional change in the rate of displacement of the output torque shaft. Thus undesired "hunting of the load driven by the output shaft is reduced to a minimum.

The rotor of unit ii may drive a serrated disc it which, when rotated, permits light impulses from the filament oi a lamp or other illuminant ii to fall on a photo-electric cell it and the irequency of light impulses on this photo cell determines (through suitable thermionic means) the field strength of the motor l 2.

Referring to Figure 3, it will be observed that the motor it has two fields. Que field lib is energised from a suitable D. 0. supply and its strength is adjustable by means of a rheostat it. A second field i211 is energised by the generator l9. -The generator i3 may be driven either by the transmitter part of the equipment, or by the movement of the gun or any associated part of either system.

The generator i9 is of the type which direct current of unchanging polarity irrespective of the direction of its mechanical drive, such direct current being in magnitude proportional to the speed of the drive. In Figure l the elements it, ll, it are illustrated that they could be replaced by the generator 99. In Figure 3 the generator it is diagrammatically indicated in order to maintain the simplicity of the circuit diagram, since electrically the effect obtained is equivalent. Inv the specification of co-pending patent application No. 435,355, now Patent No. 2,422,197, there is illustrated and described an electrical circuit designed to produce from a pulsating input, an output of electrical power in magnitude proportional to the frequency of such input pulsations. It may here be mentioned that a suitable electrical circuit has connections from the cell E8 to a pentode valve and a power tri-ode valve. The power tri-ode is choke capacity coupled to the aforementioned pentode, and the characteristic is arranged to give amplification proportional to the frequency of the light impulses falling on the photo-electric cell it. The output from the power tri-ode is fed via a centre tapped transformer to a full wave rectifier, and after smoothing by a choke and condensers, a D. C. voltage is obtained across the field i2a associated with armature it in Figure 3, which voltage is proportlonal to the frequency of the light impulses falling on photo-electric cell l8, that is, proportional to the speed of the signal or transmitter, or the speed of the gun motion.

The electrical apparatus here briefly described as associated with the elements It, I i and I8 supplies and it will be understood 6 is in Figure 1 to be considered as located within the thermionic amplifier 7. Such apparatus is then alternative to the generator i9 referred to above.

Prior to indicating in greater detail the nature or the thermionic amplifier employed, it will be useful to consider the general function of the apparatus so far described. Through the then: mionic amplifier i the fine initiating or transmitting unit 2 and the fine repeater or resetting unit t are connected so that, with their rotors in a particular position, they are in phase with one another and their total resultant effect is zero. This position corresponds to coincidence and the movement of the fine transmitter from the coincident position results in progressive angular displacement of the repeater unit 6 in the one direction or the other. Eiuch progressive displacement, by virtue of the arrangement of the thermionic amplifier, produces an output therefrom which is proportional to the degree of the displacement and the direction of which is likewise controlled according to the direction of such displacement. In actual practice, it is found possible to make the electrical arrangement such that four angular degrees of displacement between the fine units produces maximum output from the amplifier.

The relative arrangement of the coarse transmitting unit l and the coarse cancelling unit 5 is the same as that of the fine, but that part of the amplifier which deals with the coarse transmission is such that it may override the sheet of the line transmission, and when coincidence is disturbed as between the coarse transmitter and the coarse receiver, the output from the thermionic amplifier depends solely upon the coarse transmission. Preferably, one complete revolution of the coarse transmitter corresponds to 360 of movement of the associated gun mounting. Gne complete revolution of the fine transmitter corresponds to 1/11 revolutions of the gun mounting (where, of course, n is greater than 1) with the gear ratio as above referred to. For reasons which are obvious, it will be seen that the whole range of cyclic variations in the hue transmission. i. e. one revolution 01 the fine transmitter, must be equal to, or slightly greater than, the transmission step of the coarse transmission, the expression transmission step here being taken to mean the range of operation of the transmitter within which it is possible to displace the transmitter without producing conditions in the corresponding receiver which cause the latter to follow up the movements of the transmitter.

The electric motor it has its field winding, or a field winding, supplied with current in magnitude proportional to the speed of operation of the transmitter or receiver end of the system by employment of the described generator ill or the photo-electric device having the elements 118, ii and iii. The whole of the field of the motor is not supplied in this way since, of course, it may be desired for the motor to run. whilst the transmitting end of the system is stationary, where, for example, it is necessary for the motor to run in order to bring the receiver into coincidence with the transmitter under these circumstances. Nevertheless, the predominating field of the motor is the variable component indicated, with the result that there is a synchronising force exerted between the transmitter and the receiver ends of the apparatus not wholly dependent merely upon angular displacement therebetween. This synchronising force is combined as a component 7 with that further component obtained through until such time as the movement can, in fact.

take place.

With regard to the nature of the thermionic amplifier, reference will now be made to Fi ure 3. It may be divided into three separate parts. There is the first part associated with the fine transmission units 2 and d and shown at the left in Fig. 3. The electric current supplied to the rotors of units 2 and is derived by way of transformers T and T the secondary windings of which respectively go to the grids of thermionic valves V and V there being one valve in respect to each Selsyn unit. By virtue of the transformers, when there is a phase displacement in a particular direction, as between the two transmitter rotors, an alternating control potential is injected into both associated valves on the grids thereof. It is to be noted that as the electrical arrangement is such that displacement of one rotor in relation to the other gives rise to variation in grid potential of a thermionic valve there is no mechanical reactive component on the rotors of the units and consequently displacement between the rotors does not give rise to mechanical loading of the transmitter of the system.-

Depending upon the direction of such phase displacement, the injected alternating potential initiates the operation of one valve or the other. The grids of valves V and V are suitably biassed by transformers 'I and T thereby causing the valves to function in the above manner due to the phase displacement of the rotor circuit adding to or subtracting from the permanent grid bias of 'I' andT The anodes of the valves V and V are respectively connected to transformers I and T. The secondaries of these transformers connect to the grids of valves V and V respectively. These valves may be of the type sold under the registered trade-mark Thyratron. The valves V and V associated with the motor armature circuit of the motor I! constitute the second part of the amplifier, the grids of which are arranged to be controlled by the plate current of the valves V and V associated with the rotors of the units 2 and 6, it will be observed that the valves V and V are arranged so that their outputs to the motor armature l2 are in relatively opposite directions. Thus when the anode current of the one of the valves V and V increases-with, of course, corresponding decrease in the anode current of the other-one of the two valves V and V operates to supply a working current to the armature i2 in a particular direction. When the other of the valves V and V has an anode current increased, then the other of'the valves V and V operates to supply a working current in the opposite direction, to said armature 2. The motor armature thus receives current in the one direction or the other corresponding to the direction of phase displacement between the rotors, and to a degree depending upon the extent of such displacement.

iii)

The field lid of the eectric motor. as already indicated above, in the illustrated circuit is shown, for the sake of simplicity as being supplied from a generator 19. There may be a further field winding it!) upon the electric motor supplied from some exterior source and adjusted by means of a potentiometer 2d to some suitable value sufficient to prevent total'de-energisation of the electric motor. The adjustment of the otherwise constant field provided by the winding lZb of the electric motor will permit adjustment of the synchronising force introduced into the system as a whole. l

The coarse transmitting units 6 and 5 similarly have their rotors interconnected through transformers 'l. and ".IL and the secondaries of these transformers are connected to the grids of valves V and v the same arrangement of grid biassing being used by means of transformers T and T The anodes of valves V and V respectively connect to contactor operating coils C. F. and C. R. When one or the other of these contactor coils is operated on account of rotors i and 5 being out of alignment more than a predetermined amount, they open corresponding contacts C. F. and C. R. in the grid circuit of valves V and V thereby overriding any function of the fine Selsyn units 2 and ii.

Each of the contact breakers C. R. and C. F. is in practice bridged by a feed resistance so that when, say, the contact C. F. is opened by the corresponding relay coil 0. R, then the grid control potential of the valve V is lowered to a point where the valve fires fully and gives its maximum output. The efiect of varying anode current from the valves V and V will not efiectively alter the conditions within the valve V under these circumstances and it will continue to give its maum output until the contact breaker'C. F. resumes its closed position which will occur when the rotors i and 5 regain alignment. 7

Another method of introducing lag correction is shown in Figure 2 in which as in application Serial No. 435,349, now Patent No. 2,412,366, a differential gear 22 is interposed between the motor i2 and the amplifier M, which amplifier with correction unit 26 is the same as described with reference to Figure 1. That is to say, the hydraulic power amplifier unit it has a control valve BM pperated by the side member 102 of a difierential gear as a result of rotational movement of the input shaft, one sun member I03 of the difierential gear being in driven connection with the sensitive low torque input shaft I04. The output shaft ill is assumed to be connected to the mass to be moved, e. g. the gun, through the medium of a gear, which-according to known practice can include an irreversible worm to prevent the gun from driving back on the output shaft ill.

The side member 802 meshes with and drives a pinion till, the latter being secured to a shaft m8 coupled with the valve and located in suitable bearings and having a worm thread 520 in threaded engagement with a correspondingly threaded stationary nut member I25, rotational movement of the shaft we thus causing the valve not only to be turned about its axis but to be moved longitudinally to effect the owning and closing move ment, thus controlling the inflow of oil to the unit, the pinion Nil being of a sumcient width to permit of such longitudinal movement without disiggagement of the teeth of the members It! and When the input shaft "it is turned initially, the side member I02 0! the diflerential gear will be displaced by reason of the load imposed on the output shaft Hi which is solid in relation to the sun gear member H8 with which meshes a. planet wheel H4 carried by the side member H9 fixed in relation to the side member I02. The

lanet wheel I ltmeshes with the planet wheel i ll carried by the side member I82 and meshing with gear wheel 383 fixed to the input shaft I06 which passes idly through the side member N12. The said displacement of the side member it will cause a corresponding longitudinal displacement of the valve till, to permit oi the inflow of the operating fluid, which displacement will continue until the high torque output shaft ill gains the speed of the input shalt ti l, when the valve will remain in that position The side member till of the difierential gear, which also controls the correction unit in a manner similar to previously described with reference to Home l, thus has a displacement proportional to the speed of the output shaft iii and also proportional to the lag in the hydraulic amplifier The input shaft ltd is controlled so regards its amount or angle of rotation by remote control means which, as shown diagrammatically embodies coarse and fine Selsyn re-setter units 5 and 6 respectively. These Selsyn units are connected to like initiating units i and 2 via the amplifier l and have combined therewith the photo-electrical cell means it; ill and to (disc it alone being illustrated in Figure 2), in the same manner as described with reference to Fisure 1. The fine Selsyn unit 8 controls the elec tric motor it which, through the medium of the differential gear 22, drives the input shaft 50%. The purpose of the supplementary differential gear-22 is to correct for the log.

The differential gear 22 is identical with the already described difierential gear of the hydrau= lic motor i l, and in this difierential gear 22 the input and output sun gear members are indicated by the reference numerals Hide and H3?) respectively, the side members by the reference nu morals tom and Mild, and the planet members by the reference numerals 3 its and till).

The hydraulic power amplifier or motor M em= bodies the known arrangement of parallel axis cylinders ill in a block lilo, the valve illl establishing and cutting on the iiow oi, pressure fluid to the valve controlled ports of these cyl inders, and the cylinders accommodating pistons lilo connected by rods lilo to the angle box: lid, with the result that the cylinder block lilo is caused to rotate when the pistons are displaced by fluid pressure, the cylinder block carrying the output shaft round with it,

The step-by-step operation of the mechanism shown in Figure 2 is as follows: Assuming the input shaft lot to be turned clockwise the sun member till; attached thereto will rotate the pim ion ti l which, with the co-operating planet wheel ti l will have a translative movement imparted to it about the other sun member H3, thereby causing the side member N32 to rotate in, say, a clockwise direction, pinion it? thereby causing the hydraulic control valve Hill to be given a combined rotary and longitudinal movement, admitting fluid to the cylinders ii? and causing the cylinder block to rotate the main output shaft 1 l l in an anti-clockwise direction. As aforesaid, the shaft ill nection with the toothed shaft input shaft 104 is stopped or H2 so that ii the deceiereted, plant lit whereupon the rotation l tion the receiving end whl is in driving con-- 7 pinions it, 4' cause the crown wheel or side member I02 to rotate in on anti-clockwise direction, thereby restoring the sliding valve IN to its original position and bringing the apparatus to rest,

It will thus be seen that when theinput shaft llll is rotated through 10 and then brought to rest, the output shaft ii i is correspondingly turned through 10 and comes to rest.

It will also be appreciated that the relative angular displacement between the shaft i 04 and the shaft i l i determines the amount of opening of the valve idi, and therefore that for a given outout torque, an increase in the speed of the shaft ill is due to an increase in the leg or angular displacement between shafts int and l l l The aforesaid differential 22 is, as aforesaid, primarily introduced to correct for lag, for which purpose the side member i i la is in constant mesh with a gear wheel iSSct driven by the output shaft til oi the small hydraullc power amplifier or correction unit it, which as in the arrangement shown in Figure l, is a miniature of the main power amplifier M. The input shaft 3l of this small auxiliary unit it is therefore driven oh the valve spindle Hill, e. g. via gear members 18b and 12th, the valve spindle its being slidable axially in bearings in the unit ii. The supply" and return conduits for the unit iii are indicated by the reference numerals i25= Thus, any rotation imparted to the side member 802 operates a. valve in the unit 2i operation of the main valve tilt and the side member 9a of the supplementary differential gear 22 has imparted to it a movement proportional to the movement of the side member I82 of the main difierential gear; and provided there is still available a translative displacement of the valve it, this drive of the side member liQct will introduce the extra movement to the side member M2 to complete the motion of the valve Hit, of the input shaft 608 oi the small unit it will he stopped with conseouent coming to rest of the small unit. 4

It will. be understood that the constructional form of the invention may be modified in various ways. so desired, or if thought necessary, the electric motor may be provided with a, brake of any known kind capable of loading the latter proportional to its speed. For example, in order to ensure a smooth transmission of power from the motor 52 to the input shaft tilt irrespective of the variations in torque required to move the shaft ill-t, an artificial load in the form of an electric generator 82 is coupled to the motor 82, the field winding oi the generator being permanently energised and the armature virtually short circuitcd, the power absorbed by the generator being many times greater than the variations in torque which may arise in the shaft lfi i.

It is of importance to note that with the described apparatus a complete recording and wrapup system is embodied in the transmission itself, in the sense that should the thermionic ampliher be out of operation temporarily and should the director at the transmitting end he moved, then as soon as the amplifier comes into operaline up with the transmitting end.

It is also important to observe that mechanical load reaction on the electric motor may have the effect of tending to accelerate or decelerate this motor without, in any way, disturbing the transmission system as such, since any incorrectness caused by the reaction or the load will be apprein a like manner to the.

i2 means and said field winding, an hydraulic swashplate power amplifier having an input means controlled \the mechanical output of said motor and an output means adapted to drive a gun or other mass to be remotely controlled, and means responsive to relative displacement between said input means and said output means, and interconnecting said output means and said Selsyn lid put corresponding in magnitude and direction to the degree and direction of relative angular displacement of said rotors with respect to their stators, means responsive to such electrical output, an hydraulic swashplate power amplifier having an input means controlled by said responsive means and an output means adapted to drive a gun or other mass to be remotely controlled, and means responsive to relative dismacement between said input means and said output means, and interconnecting said output means and said Selsyn receiver unit, for varying the relative angular displacement of said rotors with respect to their stators proportionally to the relative displacement of said input and output means to ensure coincidence between the signal initiated by the Selsyn transmitter unit and the mass to be driven.

2. A power transmission system of the repeater type comprising a Selsyn transmitter unit and a Selsyn receiver unit each having a rotor and a stator, electrical connections between the rotors of said units, a thermionic amplifier disposed in said connections to produce an electrical output corresponding in magnitude and direction to the degree and direction of relative angular displacement of said rotors with respect to their stators, an electric motor, connections between said elecreceiver unit, for varying the relative angular displacement of said rotors with respect to their stators proportionally to the relative displacement of said input and output means to ensure coincidence between the signal initiated by the Selsyn transmitter unit and the mass to be driven.

4. A power transmission system of the repeater type comprising a Selsyn transmitter unit and a Selsyn receiver unit each having a rotor and a stator, electrical connections between the rotors of said units, a thermionic amplifier disposed in said connections to produce an electrical output corresponding in magnitude and direction to the degree and direction of relative angular d-isplacement of said rotors with respect to their stators, means responsive to such electrical output, an hydraulic swashplate power amplifier having an input shaft controlled by said responsive means tric motor and said thermionic amplifier for applying the output from the latter to the motor, anhydraulic swashplate power amplifier having an input shaft driven by said motor and an output shaft adapted to drive a gun or other mass to be remotely controlled, means for controlling the direction and speed of rotation of said output shaft in accordance with the direction and amount of displacement of said control means from a neutral position, means responsive to relative displacement between said input and output shafts for moving said control means from and to said neutral position, and means responsive to relative displacement between said input and output shafts, and interconnecting said output shaft and said Selsyn receiver unit, for varying the relative angular displacement of said rotors with respect to their stators proportionally to the relative displacement of said input and output shafts to ensure coincidence between the signal initiated by the Selsyn transmitter unit and the mass to be driven.

3. A power transmission system of the repeater type comprising a Selsyn transmitter unit and a Selsyn receiver unit each having a rotor and a stator, electrical connections between the ro- Y tors of said units, a thermionic amplifier disposed in said connections to produce an electrical output corresponding in magnitude and direction to the degree and direction of relative angular displacement of said rotors with respect to their stators, an electric motor having an armature and a field winding, connections for applying the output of said thermionic amplifier to said armature, means responsive to the speed of operation of the system to produce an electrical output and an output shaft adapted to drive a gun or other mass to be remotely controlled, a control valve "for said hydraulic amplifier, means for varying the setting of said valve in accordance with variations in the velocities of said input and output shafts, a movable member responsive in its movements to the degree of ofi'set of said valve from a neutral position, and a connection between said member and said means responsive to the output of said thermionic amplifier for advancing said responsive means by an amount proportional to the lag between the input and output shafts of a said hydraulic amplifier.

5. A power transmission system of the repeater type comprising a first pair of Selsynunits, one being a transmitter unit and the other a receiver unit and each having a rotor and a stator, a second similar pair or Selsyn units, geared connections between the two transmitter i units, geared connections between the two reproportional thereto, connections between said ceiver units, electrical connections between the rotors of said first pair of units, electrical connections between the rotors of said second pair of units, a first thermionic valve circuit disposed in said connections between the rotors of said first pair of units, said first thermionic valve circuit having an output proportional in direction and magnitude to the direction and degree of rela-. tive angular displacement of the rotors of said first pair of units with respect to their stators,

a second thermionic valve circuit, connections between said first and second thermionic valve circuits, a third thermionic valve circuit disposed in the connections between the rotors of said second pair of units, switch means in said second circuit and under the control of said third circuit for producing an output from said second circuit in one direction or the other depending upon the direction ofrelative angular displacement of the rotors of said second pair of units with respect to their stators, means responsive to the output from said second thermionic valve circuit, an hydraulic swashplate power amplifier having an input means controlled by said responsive means and an output means adapted to drive a 'gun or other mass to be remotely controlled, and means responsive to relative displacement between said input means and said output means, and interconnecting said out- 13 put means and the Belsyn receiver unit of said first pair of units, for "win: the relative annuler displacement of the rotors of said first pair or units with respect to their stators proportionally to the relative displacement of said input and output means.

REFERENCES CITED The following references are of record in the file of this patent:

Number 15 Number 14 UNITED STATES PATENTS Name Date Kiunlnsky Dec. 29, 1914 Hewlett et al. Sept. 11, 1928 Mitts; et al May 8, 1934 Davis Oct. 23, 1934 Edwards Jan. 1, 1935 Wittkuhns Apr. 30, 1935 Rachel Jan. 30, 1940 Hill Feb. 27, 1940 'I'hncker Sept. 30, 1941 Fischer Nov. 11, 1941 FOREIGN PATENTS Country Date Great Britain Apr. 23, 1937 Great Britain July 22, 1938 

